The present invention pertains to method and apparatus for measuring a wavefront of a beam of radiation. In particular, the present invention pertains to method and apparatus for measuring a wavefront of a beam of radiation having a large slope variation for use in applications including, but not limited to, characterization of optical quality of optical elements and systems, and diagnosis of eye function.
As is well known, a wavefront sensor provides comprehensive measurements relating to a wavefront of a beam of radiation, and can therefore be used to characterize the optical quality of optical elements and systems. Traditionally, such wavefront sensors include an interferometer and, recently, much use has been made of a xe2x80x9cHartmann-Shackxe2x80x9d sensor.
An interferometer-based wavefront sensor requires a high quality reference beam having substantial coherence length and sub-wavelength stability. A Hartmann-Shack-based wavefront sensor is preferred over the interferometer-based wavefront sensor because: (a) the Hartmann-Shack-based wavefront sensor does not require a reference beam; and (b) it is easier to use outside of a laboratory environment. As is well known, the Hartmann-Shack-based wavefront sensor comprises a lenslet array disposed in front of a CCD camera, and it measures the tilt distribution of ray bundles associated with the wavefront to be measured. A perceived advantage of the Hartmann-Shack-based wavefront sensor is its simplicity and reliability. Among the key parameters which are involved in using a Hartmann-Shack-based wavefront sensor are: (a) sensitivity to resolve minimum wavefront tilt; (b) dynamic range to cover the maximum wavefront tilt; (c) spatial resolution; and (d) sampling time.
The Hartmann-Shack-based wavefront sensor has been used for adaptive optics applications in astronomy. In such applications, a short sampling time (for example, less than 30 ms) is desirable to follow fluctuations caused by air turbulence, and small dynamic ranges (for example, less than 1 mR) are sufficient. However, for other types of applications, much larger dynamic ranges are required, while relatively longer sampling times can be acceptable. One example of such other applications is a comprehensive measurement of eye aberration errors useful for eye diagnosis. In particular, wavefront measurement data can be used to guide photorefractive surgery to achieve optimal results from surgery. In such an application, a wavefront measurement apparatus is expected to measure a wavefront over a dynamic range of xc2x160 mR with a tilt resolution of 0.1 mR. Such a dynamic range is well beyond the results obtainable from current Hartmann-Shack-based wavefront sensors.
As one can readily appreciate from the above, a need exists in the art for method and apparatus for measuring a wavefront over a wide dynamic range, and with small tilt resolution.
Embodiments of the present invention advantageously satisfy the above-identified need in the art, and provide method and apparatus for measuring a wavefront over a wide dynamic range, and with small tilt resolution.
Specifically, one embodiment of the present invention is an apparatus for measuring a wavefront of a beam of radiation at a plane which comprises: (a) a moving boundary locus apparatus disposed before the plane; (b) a two-dimensional photodetector array comprising a plurality of photodetector elements disposed in the plane, wherein each photodetector element produces a time varying signal in response to movement of a portion of the moving boundary locus apparatus; (c) a synchronizer adapted to synchronize each of the time varying signals with a position of the portion of the moving boundary locus apparatus; and (d) an analyzer, responsive to synchronized time varying signals output from the synchronizer, to measure the wavefront of the beam.